Gotta say, that's some ********. Prostitution can't be the world's oldest profession, because prostitutes get paid in one shape or form. How was the first prostitute paid? The John had the first profession, by providing food/shelter in excess and then using that excess to collect less necessary things, he made it his source of "income" in a sense.

the first prostitute was probably paid with food, ergo it is one of the oldest profession but not the oldest. how ever both monkeys and penguins have prostitutes and they have been around longer then humans so ..have at you.

Then the person providing food, shelter, or land had a profession first because they had that commodity to sell. The hunter sells his food, the renter/builder sells a portion of the house, and the property trader sells his land.
For the prostitute to get paid for sex, there has to be payment coming from somewhere else. "Somewhere else" is the location of a profession older than prostitution.

No, but once you give someone part of that cave in exchange for something you become a property owner with rights to renting. Essentially, you become a caveman real estate agent.
A prostitute (we'll call her Sprinkles) trades sex for things she needs (at least in this argument). The client (we'll call him Urg because he's a caveman) survives by picking berries and hunting deer. Sprinkles can't hunt deer of her own, and she needs a cave to sleep in. She finds Urg, and asks shelter. Urg requests sex. Those two now have the professions of prostitute and homeowner. The next day, Sprinkles needs food. Urg has only gotten enough for himself, so Sprinkles goes out to find someone with more. A second client (Ooga) hears of Urg's trade, and wants sex as well. That morning, he goes out and kills 2 deer instead of just one. He then trades that deer for sex with Sprinkles. Because Ooga forgoes survival, gathers a surplus, and then distributes said surplus to bring him things not necessary to personal survival (because they're selling sex for pleasure, not procreation) and therefore has given himself the profession/occupation/job of hunter.